Some tree frogs contain a chlorine compound in their skin that is a very powerful pain killer. This chemical, when used in small doses, has no side effects; in large doses, however, it is fatal.

Chlorine

Atomic Number:

17

Atomic Radius:

175 pm (Van der Waals)

Atomic Symbol:

Cl

Melting Point:

-101.5 °C

Atomic Weight:

35.45

Boiling Point:

-34.04 °C

Electron Configuration:

[Ne]3s23p5

Oxidation States:

7, 5, 1, -1

History

From the Greek word chloro, greenish yellow. Discovered in 1774 by Scheele, who thought it contained oxygen. Chlorine was named in 1810 by Davy, who insisted it was an element.

Sources

In nature it is found in the combined state only, chiefly with sodium as common salt (NaCl), carnallite, and sylvite.

Properties

It is a member of the halogen (salt-forming) group of elements and is obtained from chlorides by the action of oxidizing agents and more often by electrolysis; it is a greenish-yellow gas, combining directly with nearly all elements. At 10°C one volume of water dissolves 3.10 volumes of chlorine, at 30°C only 1.77 volumes.

Uses

Chlorine is widely used in making many everyday products. It is used for producing safe drinking water the world over. Even the smallest water supplies are now usually chlorinated.

It is also extensively used in the production of paper products, dyestuffs, textiles, petroleum products, medicines, antiseptics, insecticides, food, solvents, paints, plastics, and many other consumer products.

Most of the chlorine produced is used in the manufacture of chlorinated compounds for sanitation, pulp bleaching, disinfectants, and textile processing. Further use is in the manufacture of chlorates, chloroform, carbon tetrachloride, and in the extraction of bromine.

Organic chemistry demands much from chlorine, both as an oxidizing agent and in substitution, since it often brings many desired properties in an organic compound when substituted for hydrogen, as in one form of synthetic rubber.

Handling

Chlorine is a respiratory irritant. The gas irritates the mucus membranes and the liquid burns the skin. As little as 3.5 ppm can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths. In fact, chlorine was used as a war gas in 1915.